The present invention relates to an electromagnetic flowmeter for measuring the flow rate of grout and concrete used in the construction and building areas.
It is very important to measure the flow rate of grout accurately when it is forced by pressure into soil for soil stabilization. Undergrouting cannot achieve ground improvement, and overgrouting not only results in waste of grout but also brings about accidents such as deformation of ground, spouting of grout through soft beds and underground openings, and lifting and leaning of existing structures such as dams and buildings. The quantity of grout to be forced should be changed according to the type of soil. For accurate measurement of grout fow rate, the electromagnetic flowmeter recently has come into general use because of its feature that it has no complex mechanical parts in the conduit that carries the fluid to be measured. Unlike conventional differential pressure type and vane-wheel type flowmeters, the electromagnetic flowmeter has no orifice nor revolving body which projects into the conduit and causes pressure loss or gelation of grout.
In spite of this advantage, the commercial electromagnetic flowmeter as shown in FIG. 1 suffers from a disadvantage when used for grouting. In FIG. 1, grout is adjusted to a proper concentration by the mixer (1a), stored in the tank (1b), and then forced by pressure into soil by the pump (2) through the rubber hose (3), the electromagnetic flowmeter (4), and the pipe (6) fitted to the boring machine (5). The electromagnetic flowmeter is made up of the rubber-lined stainless steel pipe (7), the flanges (8) attached to both ends of the pipe for connection of the rubber hoses (3), the coil (9) and iron core (10) placed outside the pipe (7), and the electrode (11) attached to the pipe (7). The coils, iron cores, and electrodes are encased in the casing (12), (13). The grout which is forced by pressure through this electromagnetic flowmeter tends to settle and adhere to the pipe (7) and electrode (11) due to its inherently high consistency and ease of solidification. The deposited grout has to be removed frequently by water washing; otherwise, it will gel to form a film which results in errors in measurements. When grout settles on the inner wall of the pipe (7), the electromagnetic flowmeter (4) has to be discarded entirely because it is impossible in practice to exchange the pipe (7) alone. Moreover, it is difficult for the conventional electromagnetic flowmeter to measure the flow rate of fluids at pressures higher than 150 kg/cm.sup.2, because the connection by flange (8) of the electromagnetic flowmeter (4) and the rubber hose (3) is not strong enough and the sealing between the electrode (11) and the pipe (7) is not complete.